According to a generally used electrocardiograph, the potential change of six points on the chest over a period of time is measured and represented on a graph with time as the abscissa and the potential the ordinate, whereby the heart disorder is detected from the wave form obtained relative to each point. However, with an electrocardiograph of this type, it is difficult to accurately examine the whole electrical activity of the heart. And according to a recently developed electrocardiograph, 80 to 200 electrodes are applied to various points of the body surface near the heart and the potential of each point is measured, whereby the electrical activity of the heart is synthetically judged.
By this electrocardiograph, an isopotential map for a certain time is made for the body surface near the heart, as shown in FIG. 1. In this isopotential map, the body surface potentials are shown on isopotential lines so as to make it possible to examine the distribution of the body surface potentials. This isopotential map is obtained e.g. by temporarily storing the potential of each electrode in a memory unit, calculating the isopotential points based on the potential of each electrode through a computer, and then drawing the isopotential lines e.g. at a pitch of a few tens of microvolts on a television or a XY-plotter.
When using this electrocardiograph, a plurality of isopotential maps are obtained at intervals of the sampling time and the enlargement or contraction of the positively and negatively charged parts of the body surface near the heart can be recognized from the change of the potential gradient, whereby the electrical activity of the heart is indicated.
However, in the electrocardiograph of this kind, it is difficult to apply a number of electrodes to the points of the body surface with small contact resistance, and to stably and correctly detect the potential of each point.
For example, it takes four persons as long as 30 minutes to 1 hour to correctly place the conventional suction type electrodes at about 100 points of the body surface, and only one or two patients can be examined under an hour even in the best conditions.
It is necessary that the electrodes of an electrocardiograph be applicable to any person, adult or child, male or female, having different body shapes. The electrodes must be free from errors in potential measurement due to the unevenness of the body surface or its upward and downward motion caused by the breathing. Further, the electrodes are required not to cause any terror, pain or sense of oppression to patients. Further, they must be able to be applied or removed easily and rapidly, and to be easily maintained. Furthermore, it is necessary to place the electrodes correctly relative to one another and without deviation.
In detecting the potentials of the points on the body surface, preferably all the electrodes are pressed onto the body surface with a strong force so as to stably and correctly measure the potentials at the electrode contact points. However, in an electrocardiograph for detecting the potentials of many points the human body, a number of electrodes are employed. And if the pressure applied for an electrode is 500 g and 100 electrodes are used, a force as strong as 50 kg is applied to the body in the area where it necessarily gives a strong sense of oppression to the patients. Therefore, such an electrocardiograph is extremely unsuitable for examining the heart of a patient having reduced strength.
Consequently, practically usable electrodes cannot be obtained simply by increasing the force with which the electrodes are pressed onto the body.
In a conventional electrocardiograph, since signals fed from each electrode are amplified and shown in a graph, the bad contact of electrodes can be easily recognized from the graph for the particular electrode.
However, in the improved electrocardiograph described above, an isopotential map of the body surface at the time of measurement is shown, and therefore, it is more difficult than in the conventional electrocardiograph to judge from the map whether there is bad contact of electrodes. Consequently, in order to examine the heart with a high accuracy, all the electrodes must be always in sure electrical contact with the body surface. If a conventional suction type electrode or an adhesive tape type electrode makes bad electrical contact for one second per 100 seconds, on the average one of the 100 electrodes is always in bad contact and accurate measurement cannot be performed.
It is known that an electrocardiograph which produces an isopotential map of the body surface near the heart can indicate more accurately the electrical activity of the heart than a conventional electrocardiograph which shows only the change of the voltage of the measuring point. However, with such an electrocardiograph, potentials of a large number of points on the body surface must be detected simultaneously and accurately. Since this problem has not yet been sufficiently overcome, the electrocardiograph of this type has not yet come into widespread use.